efeitos alelopáticos do eucalyptus citriodora sobre ...2007/2008). amaryllis plant cv. belinda...

Planta Daninha, Viçosa-MG, v. 27, p. 887-899, 2009. Número Especial

887Allelopathic effects of Eucalyptus citriodora on amaryllis ...

1 Recebido para publicação em 2.10.2008 e na forma revisada em 11.12.2009.2 Botany Dept, National Research Centre, Dokki, Cairo, Egypt; 3 Ornamental Plant and Woody Trees Dept., National ResearchCentre, Dokki, Cairo, Egypt, <[email protected]>, El Buhoth St.., Dokki, cairo, Egypt. Postal Code: 12311; Tel: (+202)

33371362 /433/615/933/449; Fax (+202) 33370931.

ALLELOPATHIC EFFECTS OF Eucalyptus citriodora ON AMARYLLIS AND

ASSOCIATED GRASSY WEED1

Efeitos Alelopáticos do Eucalyptus citriodora sobre Amarílis e em Gramíneas Daninhas

Associadas

EL-ROKIEK, K.G.2 and EID, R.A.3

ABSTRACT - A Petri dish assay was carried out for screening different concentrations ofaqueous extracts of fresh and dry leaves of Eucalyptus citriodora on germination and seedlinggrowth of wild oat weed (Avena fatua). Seed germination, root and shoot length of wild oatexhibited different degrees of inhibition according to the concentration of the aqueous extract.Maximum inhibitions of germination percentage, root and shoot length were recorded whenusing 25% fresh leaf extract. Based on this preliminary work (Petri dish assay), studies wereconducted under greenhouse conditions at the National Research Center, Egypt, in the twowinter seasons of 2006/2007 and 2007/2008 to evaluate the effects of foliar and soil treatmentsof aqueous extracts of Eucalyptus citriodora fresh and dry leaves on wild oat weed as well ason the growth and flowering of amaryllis (Hippeastrum hybridum), compared with therecommended dose of the herbicide tralkoxydim. Amaryllis fresh and dry weights as well asflowering increased significantly when treated with the previous extracts, especially thefresh leaf extract. However, the fresh and dry weights of wild oat were significantly reducedby the aqueous extracts, either fresh or dry, indicating phytotoxic effects. Tralkoxydim causedcomplete inhibition of wild oat as compared with the control. The studies involved estimationof the endogenous contents of total phenols in weed. With all the treatments, the inhibitoryeffects on weeds were correlated with accumulation of the internal contents of total phenols,compared to their respective controls. The amount of phenols correlated well with the weed’sgrowth performance. This study establishes the effect of the aqueous extracts on the weedwild oat, associated with amaryllis, which may serve as a tool in establishing their herbicidalpotential.

Keywords: aqueous extract, herbicide, phytotoxic, total phenols, tralkoxydim.

RESUMO - Um experimento em placas de Petri foi realizado para a seleção de diferentes concentraçõesde extratos aquosos de folhas frescas e secas de Eucalyptus citriodora na germinação e nocrescimento inicial de aveia-selvagem (Avena fatua). A germinação da semente, a raiz e o comprimentoda brotação apresentaram diferentes graus de inibição, de acordo com a concentração do extratoaquoso. As maiores porcentagens de inibição da germinação, de raiz e de comprimento de brotaçãoforam registradas com extrato fresco das folhas a 25%. Com base no trabalho preliminar (experimentoem placa de Petri), foram conduzidos estudos na estufa do Centro de Pesquisa Nacional, Egito, em

duas estações de inverno: 2006/2007 e 2007/2008. Nesse local, foram avaliados os efeitos detratamentos foliar e do solo de extratos aquosos das folhas frescas e secas de Eucalyptus citriodora

na aveia-selvagem, assim como no crescimento e no florescimento da espécie Hippeastrum

hybridum, em comparação com a dose recomendada do herbicida tralkoxydim. Os pesos frescos esecos do amarílis sofreram aumento significativo, bem como o florescimento, quando tratados com os

extratos, principalmente com a pulverização do extrato das folhas frescas. Entretanto, os pesosfrescos e secos da aveia-selvagem foram reduzidos significativamente pelos extratos aquosos, tantofrescos como secos, indicando intoxicação. O herbicida tralkoxydim causou a inibição completa de

EL-ROKIEK, K.G. and EID, R.A.


888

aveia-selvagem em comparação ao controle. Os estudos envolveram a avaliação dos índices endógenosde fenóis totais na espécie daninha. Em todos os tratamentos, os efeitos inibitórios nas espéciesdaninhas foram correlacionados com o acúmulo de índices internos dos fenóis totais, comparadosaos respectivos controles. Constatou-se boa correlação entre a quantidade de fenóis e o desempenhodo crescimento na espécie daninha. Este estudo estabeleceu o efeito dos extratos aquosos sobre aespécie daninha aveia-selvagem associada ao amarílis, o que pode servir como ferramenta paraestabelecer seu potencial herbicida.

Palavras-chave: extrato aquoso, herbicida, fitotóxico, fenóis totais, tralkoxydim.

INTRODUCTION

Amaryllis (Hippeastrum hybridum) is anornamental bulbous flowering plant of thefamily Amaryllidaceae. It has large and showyflowers with many bright colors (Jana, 1995)and it is one of the most brilliantly coloredspring bulbs. It is suitable for planting in pots,greenhouses, gardens and landscaping. Itcan be grown under diverse environmentalconditions, ranging from tropical to subtropicalor temperate climate (Okubo, 1993; Jana,1995).

Amaryllis has long been a holiday favorite,providing a splash of Christmas red color inmid winter (not in tropical conditions such asthose found in Brazil in mid December). Thisplant will be shipped as a spiking bulb toencourage the beautiful blooming to occur.

Several taxa are used for medicinal,flavoring, psychotropic and other purposes(Meerow et al., 2000).

Weeds are one of the major constraints toplant production worldwide. Weeds affect plantgrowth and production that may be reducedsignificantly when weeds compete with themfor light, water and minerals (Hussein, 2001).Many important weed problems are similaramong the crops because of crop rotation.Thus, lack of adequate nutrition may resultin poor flowering, regardless of bulb size.

Increasing herbicide use worldwide isrelated to several regional factors, primarilyincreasing labor cost and herbicide availabilityand efficacy. Because of their environmentaland toxicological effects, besides increasingherbicidal resistance among weeds, morealternative strategies against weeds mustbe developed. This is true and valid for allcrops and economic plants grown in the

worldwide, such as amaryllis. Thus, efforts arebeing made to create new environmentally-friendly means of weed management. Usingallelopathy for weed management leadsto improved water quality and reducedenvironmental contamination. Allelopathyis understood as the effect of chemicalinteractions between plants (Muller, 1969;Gross, 1999). Rice (1984) and Lambers et al.(1998) defined allelopathy as the effect(s) of oneplant on other plants through the release ofchemical compounds in the environment.Chemical identification procedures haverecently become more advanced, andbiologically active substances with phytotoxicpotential, that can explain allelopathicbehaviour, have been found (Duke et al.,1998). The chemicals causing the allelopathiceffects are called allelochemicals.

Natural plant products known for theirstructural and chemical diversity offer achallenging new area for the discovery of newherbicides. Essential oils from a number ofhigher plants are known to possess greatertoxicity and are responsible for allelopathicactivity. Thus, volatile oils from Eucalyptuscitriodora were selected, based on their knownpesticidal and phytotoxic properties.

Previous studies have shown that variousEucalyptus species can yield allelopathicchemicals which may be effective in sup-pressing understorey vegetation. Allelopathy isassociated with Eucalyptus spp. due to thepresence of allelochemicals in these plants;several studies have demonstrated therelease of phenolic and volatile compounds inits foliage (Al-Naib and Al-Mousawi, 1976).Eucalyptus reduces the growth of neighboringcrops through the release of allelochemicals(May and Ash, 1990). The extracts of freshleaves were found to be most toxic (Al-Naib and



Al-Mousawi, 1976). It was concluded thatallelopathy is likely to be a cause of understoreysuppression by Eucalyptus species, especiallyin drier climates (May and Ash, 1990). Cao andLuo (1996) reported that aqueous extract frombark and leaf, and volatiles from leaves ofEucalytus citriodora showed allelopathic effecton the growth of nine species, including theweeds Bidens pilosa, Digitarie pertenuis,Eragrostics cilianesis, Setaria geniculata, andcrops such as corn, rice, cucumber, bean andStylosanthes guianensi. Studies were carriedout to explore the effect of volatile oils fromE. citriodora against weeds such as Phalarisminor, Chenopodium album, Echinochloacrus-galli, Ageratum conyzoides, Partheniumhysterophorus, and Amaranthus spp. Inlaboratory bioassay germination, seedlinglength, chlorophyll content and respiratoryability of weed plants was drastically affected(Batish et al., 2005).

Therefore, this study aimed to evaluatethe effect of E. citriodora aqueous extractagainst the grassy weed wild oat (Avena fatua),associated to amaryllis plants, in comparisonto the herbicide tralkoxydim and the reversalof this control on amaryllis (Hippeastrumhybridum) growth and flowering .

MATERIALS AND METHODS

Laboratory test

Eucalyptus citriodora plants were gatheredfrom Egyptian gardens. A total of 2.5, 5, 10, 20or 25 g of fresh Eucalyptus citriodora leaveswere washed with tap water followed by distilledwater to remove dust, and transferred intolabeled bottles, to which 100 mL of sterile,deionized, distilled water was added. Themixture was shaken well by hand and allowedto soak for 48 h at room temperature andfiltered to obtain Eucalyptus extracts at 2.5, 5,10, 20 and 25% concentrations. The sameweight of the previous fresh leaves was oven-dried at 40 oC to obtain the corresponding dryweight, ground into a fine powder (using anelectric mill until homogeneity was achieved)and transferred into labeled bottles to which100 mL of sterile, deionized distilled waterwas added for 48 hours. The produced extractswere collected and filtered through Whatmanno. 1 filter paper. A Petri dish assay was

carried out for screening the effect of differentconcentrations of aqueous extracts ofEucalyptus citriodora on germination andseedling growth of wild oat weed.

Seeds of wild oat were germinated inPetri dishes containing 1-layer Whatmanno. 3 filter paper with 6 mL at differentconcentrations of E. citriodora fresh and dryleaf aqueous extracts, as follows:

a- Fresh leaf extract at 2.5, 5, 10, 15, 20 and25%.

b- Dry leaf extract at 0.875%, 1.570%, 3.134%,4.702%, 6.270% and 7.850%.

c- Untreated control (distilled water).

Germination was carried out in thelaboratory in November at average maximumand minimum temperatures 25.5 ± 1 and18.5 ± 1 oC. The experiment was repeatedtwice with one week interval. Each treatmentwas represented by five replicates, with eachPetri dish representing one replicate. After fivedays, 2 mL of the previous treatments wereadded. Germination percentage, root and shootlength of wild oat seedlings were recorded10 days after germination.

Pot experiments

Pot experiments were conducted undergreenhouse conditions at the NationalResearch Center, Dokki, Cairo, Egypt, duringtwo successive winter seasons(2006/2007 and2007/2008). Amaryllis plant cv. Belinda bulbswere collected from the Agricultural ResearchCenter, Ministry of Agriculture, Giza, Egypt.The bulbs were grown in 30 cm diameter pots,filled with a soil mixture at average maximumand minimum temperatures of 25.5 ± 1and 18.5 ± 1 oC. The physical and chemicalcharacteristics of the soil mixture used forgrowing the bulbs are shown in Table 1. Thepots were infested with wild oat seeds at therate of 10 seeds per pot. Weed seeds were sownsimultaneously and mixed thoroughly at 2 cmdepth from the soil. Routine fertilizers wereadded as calcium super phosphate (15.5%P

2O

5) before planting at the rate of 3 g per pot,

representing sources of P, ammonium sulfate(20% N) at the rate of 2 g per pot and potassiumsulphate (48%, K

2O) at the rate of 1 per pot,

representing sources of N and K, respectively,were added 30 days after bulb planting.



890

Based on the preliminary work (Petri dishassay), the fresh leaf extract was used atconcentrations of 12.5 and 25% and thecorresponding dry leaf extract, as follows:

Preparation of the extract

Two hundred fifty and 500 g of fresh leavesof Eucalyptus citriodora were washed with tapwater, followed by distilled water to removedust. Leaves were transferred to labeledbeakers, to which 2000 mL distilled waterwere added and allowed to soak for 48 hours.The produced extracts were collected andfiltered through very fine (1 mm) mesh andpressed for complete extraction. This stepwas repeated with the corresponding finelyground dry leaves (oven dried at 40 οC), andrepeated according to the quantity of extractneeded.

The extracts were applied early in themorning 30 days after sowing. The treatmentswere carried out weekly thrice, as follows:

Spraying treatments

The following aqueous extracts wereapplied at the rate of 250 mL per pot.

1- Aqueous extract of fresh leaves at 12.5% and25%.

2- Aqueous extract of dry leaves at 2.9% and6.2%.

Soil treatments

The previous aqueous extracts wereapplied in the soil at the rate of 250 mL kg-1

soil.

1- Aqueous extract of fresh leaves at 12.5% and25%.

2- Aqueous extract of dry leaves at 2.9% and6.2%.

The pots were arranged in a complete blockdesign with 11 treatments. Each treatmentwas represented by 9 pots (replicates 1 pot =1 replicate). The infested weed was collectedfrom each pot at 30 and 60 days aftertreatments.

Data on amaryllis were recorded foreach individual plant at the flowering stage,including leaf length, number of leaves, freshand dry weight of leaves, flowering date, flowerstalk length, stalk diameter, flower diameter,fresh and dry weight of cut spike, fresh weightof bulbs, number of flowers/spike, and numberof bulblets.

Determination of essential oil in

Eucalyptus citriodora leaves

The essential oil was prepared by hydro-distillation (Adams, 1995): A known weight(50-70 g) of fresh leaves of Eucalyptus citriodorais subjected to hydro-distillation for 5-6 hoursusing Clevenger type apparatus for oilslighter than water. The oil yielded was driedover anhydrous sodium sulphate and storedin sealed vials at low temperature beforeanalysis.

GC/MS analysis was carried out onFinningan Mat SSQ7000 mass spectrometerdirectly coupled to a Varian 3400 GC/MSsystem, equipped with a DB-9 fused silicacapillary column (30 m x 0.25 mm i.d) usinghelium as the carrier gas with a linear velocityof 31.5 cm s-1, split ratio 1/60, ionizationenergy 70 ev, scan time 1 sec., transfer linetemp. 260 οC, oven temperature programed,

Table 1 - Physical and chemical analyses of the soil

3-Alkoxydim treatment (Grasp) at 500 ppm, Grasp [tralkoxydim,

10% Zeneca-England] with molecular formula: 2-[1-(ethoxyimino)

propyl]-3-hydroxy-5-mesityl cyclohex-2-enone.

4-Weed-free.

5-Unweeded.

Character Value

Clay 22.80%

Silt 19.00%

Sand 58.22%Physical

Texture Sandy clay loam

pH (SB) 7.63

Total nitrogen -

Available P 35 mg kg-1 soil

Available K 8 mg kg-1 soil

Fe 18.00 mg kg-1 soil

Mn 3.21 mg kg-1 soil

Zn 9.21 mg kg-1 soil

Cu 1.30 mg kg-1 soil

Chemical

Organic matter % 2.15

EC (dS m-1) 2.38



40 oC to 250 οC at 4 oC min-1. The percentagesof compounds were calculated by the areanormalization method without consideringresponse factors. The oil components wereidentified by comparing their mass spectrawith authentic compounds. Oven dried leaves(at 40 oC) were subjected to the same previousanalysis.

Determination of chemical changes in

weeds

Total phenols in wild oat weed

Total phenolic compounds in oat weedwere extracted from drying finely groundtissues (powdered). Drying was carried out inan electric oven at 60 oC until constant weightwas achieved. Total phenols were determinedcolorimetrically according to the methoddefined by Snell and Snell (1953), using Folinand Ciocalteu phenol reagent.

A- Photosynthetic pigments in amaryllis

Chlorophylls a, b and carotenoids wereextracted from fresh leaves and estimated,according to colorimetrically Wettstein method(1957).

B- Total carbohydrate contents

Total carbohydrate contents wereextracted from drying finely ground tissues(powdered). Drying was carried out in anelectric oven at 60 oC, until constant weightwas achieved. Total carbohydrates wereextracted according to Herbert et al. (1971) andestimated colorimetrically by the phenol-sulphoric acid method, as described byMontogomery (1961).

C- Nitrogen, phosphorus and potassiumcontents (NPK)

Nitrogen, phosphorus and potassiumcontents were determined in dried organsaccording to the official and modified methodsof analysis (AOAC, 1984).

Statistical analysis: The data obtained weresubmitted to standard analysis of variance; theLSD values were obtained when F values weresignificant at 5% level (Snedecor & Cochran,1980).

RESULTS AND DISCUSSION

Most allelopathy research is focused ondirect negative plant-plant interactions causedby allelochemicals. Therefore, understandingplant interactions is important to reduce thedependency on herbicide in future croppingsystems. Allelopathy plays an important rolein plant interaction in some plant species(Olofsdotter et al., 2002).

Table 2 data show that the germinationpercentage of wild oat seeds is negativelyaffected by fresh and dry leaf extract ofE. citriodora at different concentrations,compared to untreated control. Table 2 showsthat fresh leaf extract was more effective.Maximum inhibition was recorded by spraying25% fresh leaf extract when the percentage ofgermination reached 35%. Various laboratoryscreening techniques have been developedto demonstrate measure and quantify allelo-pathy without the interference of resourcecompetition (Navarez and Olofsdotter 1996;Kawaguchi et al., 1997). The results also showthat root and shoot seedlings of wild oat weresignificantly reduced by the different aqueousextracts. This inhibition was observable byspraying 25% fresh leaf extract (81.5%). It isclear that shoots were less sensitive than

Table 2 - Effect of different aqueous extracts of fresh and dryleaves of Eucalyptus citriodora on seedling root and shootlength of wild oat weed

Wild oat seedling

Treatment (%) Germination

(%)

Root length

(cm)

Shoot length

(cm)

2.50 100.0 7.50 11.44

5.00 84.4 5.64 9.56

10.00 75.2 5.26 9.10

15.00 75.8 4.50 8.04

20.00 67.6 4.10 7.10

Fresh leaf

extract

25.00 34.9 2.44 5.56

0.85 100.0 11.80 12.10

1.75 82.5 11.28 12.06

3.26 80.6 10.10 11.16

4.70 70.0 9.24 9.36

6.26 68.8 9.12 8.32

Dry leaf

extract

7.85 54.6 8.24 7.46

Control 0.0 100.0 13.18 12.54

at 5 % 2.42 0.52 0.56LSD

at 1% 3.42 0.74 0.81



892

roots (Table 2). Remarkable inhibition inseedling shoot length reached 55.7% with thesame treatment.

Pot experiments

Weeds

Results show that both fresh and dryweights of wild oat weed were significantlyreduced by applying the herbicide tralkoxydimor different extracts of E. citriodora 30 and60 days after sowing (Table 3). These resultswere true with different applications. Thereduction caused by the herbicide was higher.The highest reduction in fresh weight causedby the extracts was observed when 25% of freshleaf extract of E. citriodora was sprayed, whichamounted to 79.6 and 59.8%, 30 and 60 daysafter sowing, respectively. The dry weightreduction exhibited similar trend at bothstages.

Aqueous extracts of different species ofEucalyptus were documented by severalauthors (Al-Naib and Al-Mousawi, 1976; Mayand Ash, 1990; Cao and Luo 1996). Theresults obtained with E. citriodora leaf extractswere in agreement with previous studies(Nishirnura et al., 1982; Florentine and Fox,2003; Batish et al., 2005). In general, reducedgrowth of many weed species in response todifferent plant extracts is well reported

(Rice, 1984; Olofsdotter et al., 2002, Cheemaet al., 2003; El-Rokiek et al., 2006). High weedgrowth suppression may be attributed to thepresence of toxin compounds in the aqueousextracts, as reported by many authors (Barnesand Putnam, 1986; May and Ash, 1990;Shilling et al., 1992 and Shiming, 2005). Thesecompounds are volatile oils and phenolicacids (Bignell et al., 1994 and Lisaneworket al., 1993). Data in Table 8 may support theseresults. The herbicide caused completeinhibition of this weed. Similar results werereported by (Singh et al., 1995; Fayed et al.,1998).

Changes in phenolic contents in wild oat

weed

Table 4 results show that great differenceswere found between the total phenol contentsin weed treated with different extracts ofE. citriodora and those in untreated weed.Generally, foliar treatment applicationresulted in relatively higher contents than soiltreatment application. The results alsoindicated that accumulation of total phenolscorrelated with extract concentration.Accumulation of total phenols in wild oatdried tissues was observed after spraying25% of fresh leaf extract, at both growthstages, compared to the correspondingcontrols. Accumulation of phenols is often a

Table 3 - Effect of different aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on growth of wild oatweed (Average of the two seasons)

FW (g per pot) DW (g per pot)

DAS (Days after sowing)Treatment (%)

60 90 60 90

12.5 4.40 10.47 0.569 2.432Fresh leaf extract

25.0 2.02 6.42 0.471 1.375

2.9 6.35 11.67 1.120 2.668Spraying

Dry leaf extract6.2 3.22 7.58 0.526 1.422

12.5 4.98 13.89 0.952 3.691Fresh leaf extract

25.0 3.23 8.68 0.503 1.741

2.9 7.20 14.25 0.986 3.762

Soiltreatment

Dry leaf extract6.2 4.03 10.02 0.800 2.138

Herbicide Tralkoxydim 500 ppm - - - -

Weed-free - - - - - -

Unweeded - - 9.9 15.99 1.658 3.906

L.S.D. at 5% 0.37 0.65 0.041 0.045



characteristic of stress condition (Nemat Allaand Younis, 1995; Ahmed and Rashad, 1996;Hopkins, 1999; El-Rokiek, 2002 and 2007).

Amaryllis growth

Leaf length and number of leaves ofamaryllis plants at the flowering stage weresignificantly increased by all the appliedextracts as well as by the herbicidetralkoxydim, compared to the unweeded control(Table 5). Spraying treatments producedrelatively higher results than soil treatments.Maximum leaf length increase was obtainedwith weed-free and herbicide treatmentfollowed by spraying treatment of fresh leafextract of E. citriodora at 25%. Theseincrements reached 86.5, 84.4 and 69.7%,respectively. In addition, fresh weight ofamaryllis leaves seemed to significantlyincrease in response to all treatments ofeither fresh or dry leaf application, as wellas tralkoxydim. Maximum increase wasobtained with weed-free control and herbicidetreatment followed by 25% of fresh leaf extractspray treatment. Fresh weight increase wasaccompanied by dry matter accumulation(Table 5), compared to the untreated control.In this respect, fresh leaf extract induced thebest performance, especially at its highestconcentration. On the other hand, growthincrease of amaryllis plants treated withdifferent aqueous extracts of E. citriodora leavesor tralkoxydim was accompanied by the

corresponding decrease in fresh and dry weightof grassy weed. Many workers reported thatcontrolling weeds associated with plantsreduced competition, consequently increasingplant growth (Singh et al., 1995; Fayed et al.,1998; Kumar et al., 2005; El-Metwally andEl-Rokiek, 2007).

Amaryllis flowering

Days to first flower emergence

The time required for first floweremergence varied widely (Table 6) withdifferent treatments of E. citriodora leafextracts. The earliest first flower emergencewas obtained with weed-free control (149 days)followed by the tralkoxydim-treated plants(150 days), with the extract treatmentsexhibiting great variation (from 153 to163 days) Fresh leaf extract spray at 25%produced the most rapid flowering (153 days).The maximum time required was observed inunweeded control (164 days), i.e., unweededcontrol delayed flowering 11 days, compared tothe weed-free treatment (from153-to 164 days),with the likely explanation for this being thatweed competition reduced amaryllis growthand nutrient uptake and that these may havea role in delaying amaryllis flowering, asreported by Hussein, 2001.

Number of flowers/plant

The number of flowers per plant showedno significant response by all treatments, ascompared to the untreated control (Table 6).

Flower stalk length

Weed-free control recorded the longestflower stalk (20.20 cm), followed by thetralkoxydim treatment (19.7 cm) and the freshextract spray treatment (18.9 cm). On theother hand, the shortest flower stalk wasobtained in the unweeded control (15.8 cm),as shown in Table 6.

Flower diameter

Table 6 data indicate that the differentextracts of E. citriodora leaves had a greatinfluence on flower diameter. The largest(12.7 cm) flower diameter was obtained under

Table 4 - Effect of different aqueous extracts of fresh and dryleaves of Eucalyptus citriodora on total phenol contents inwild oat (Average of the two seasons)

Total phenols

(mg g-1 DW)

90 DAS60 DAS

Treatment (%)

33.0350.1412.5

57.2856.2925.0Fresh leaf extract

18.6132.832.9

34.6452.606.2Dry leaf extract

Spraying

18.2424.1412.5

21.4134.8425.0Fresh leaf extract

12.6212.662.9

20.2426.056.2Dry leaf extract

Soil

treatment

--500 ppmTralkoxydimHerbicide

9.7612.73--Unweeded

0.861.11L.S.D at 5%



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weed-free control and herbicide treatment, aswell as in the fresh leaf extract spraytreatments (6.9, 6.8 and 6.1 cm, respectively).The smallest flower diameter was recordedwith unweeded control (4.3 cm). The stalkdiameter results were similar.

Cut spike fresh and dry weights

A significant increase was observed in cutspike fresh weight in response to the fresh anddry leaf extract and tralkoxydim treatments.The greatest response was found with weed-free control as well as the herbicide. This effectwas also true with application of fresh leaf

extract at 25%. The pattern of change in dryweight due to these treatments was, to a greatextent, similar to that in fresh weight (Table 6).

Number of bulblets per plant

Number of bulblets per plant differedsignificantly due to the different extractapplications and herbicide treatments(Table 6). The maximum number of bulblets(2.68) was found in weed-free control followedby the herbicide treatment (2.51) and fresh leafextract spray treatment at 25% (2.32). Thelowest number of bulblets (1.2) per plant wasrecorded with unweeded control.

Table 5 - Effect of different aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on growth of amaryllis (Average of thetwo seasons)

Table 6 - Effect of different aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on fresh weight of bulbs, fresh and dryweight of cut spike, flowering characters of amaryllis. (Average of the two seasons)

FW bulbs

(g per plant)

Number of

bulbletsper plant

DW

of cut spike

(g per plant)

FW of cut

spike

(g per plant)

Flower

diameter(cm)

Stalk

diameter

(cm)

Flower

stalk length(cm)

Number of

flowersper plant

Days

to flowerbud

appearance

Treatment (%)

169.502.145.5292.005.1218.0353.434.0156.512.5

176.402.325.8295.566.1018.9156.214.0153.025.0

Fresh leaf

extract

162.432.004.2389.834.8116.4151.454.0157.02.9

171.802.145.5892.435.7717.5154.814.0152.06.2

Dry leaf

extract

157.221.873.5478.414.8016.4149.704.0163.512.5

161.581.894.1085.306.8219.5058.004.0160.025.0

Fresh leaf

extract

152.501.773.2375.624.3515.8945.634.0164.02.9

161.581.894.0085.004.8016.4048.904.0163.56.2

Dry leaf

extract

189.512.517.83100.006.8019.7358.304.0150.0500 ppmTralkoxydim

194.302.687.84101.406.8520.2060.314.0149.0-Weed-free

152.001.202.8373.204.2815.8143.284.0164.5-Unweeded

2.310.040.020.730.050.081.51NS0.5LSD at 5%

Leaves per plant (g)

DWFW

Number of

leaves/per plant

Leaf length

(cm)Treatment (%)

11.8380.019.050.812.5

12.3083.7114.055.525.0Fresh leaf extract

8.6177.917.048.32.9

11.8880.179.053.76.2Dry leaf extract

Spraying

6.8370.186.040.012.5

8.5177.536.048.225.0Fresh leaf extract

4.9450.317.032.92.9

7.2373.417.044.86.2Dry leaf extract

Soil treatment

12.9086.4714.060.3500 ppmTralkoxydimHerbicide

13.7688.5514.061.0--Weed-free

4.9349.815.032.7--Unweeded

2.310.310.83.6LSD at 5%



Fresh weight of bulbs (g)

Table 6 data show that there are greatvariations in bulb fresh weight due to theapplication of different extracts of E. citriodoraleaves and tralkoxydim, compared to thecontrol. Significant increase was obtained withall treatments. Fresh and dry leaf extractscaused a significant increase. Fresh leafextract application was superior, with fresh leafextract spray inducing the best performance,especially at its highest concentration (25%).The positive effects on amaryllis growth wouldexplain the increased flower net return(Table 6). Previous studies indicated thatincreased amaryllis growth was accompaniedby increasing flowering characters (Bose et al.,1981; Okubo, 1993; Jana, 1995; Siddique et al.,2006 and 2007).

Effect of aqueous extracts of Eucalyptuscitriodora on chemical constituents of

photosynthetic pigments

Different treatments of E. citiodora leafextracts revealed significant increase inchlorophyll a & b, and carotenoids in freshleaves of amaryllis over the unweeded control(Table 7). Tralkoxydim generally induced extraincrease of chlorophyll a & b over correspondinglevels in the plants treated with extracts. Thislevel was more obvious with weed-free control.

The results of total pigments and carotenoidswere similar (Table 7).

Total carbohydrate contents

Table 7 results show that differentEucalyptus leaf extracts caused significantincrease in the contents of total carbohydratein amaryllis leaves. Such increase wasmore remarkable due to the spray of freshleaf extract at 25%. The herbicide treatment

Table 7 - Effect of different aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on the contents of chlorophyll a, b, totalchlorophyll and carotenoids and total carbohydrate of amaryllis. (Average of the two seasons)

Total carbohydrate

contents(mg g-1 DW)

Total chlorophyll contents

(mg g-1 fresh leaves)

BulbsLeaves

Carotenoids

(mg g-1 freshleaves)

Total ChlChl bChl a

Treatment (%)

21.5046.500.6313.691.512.1812.5

23.3048.900.7944.121.772.3525.0Fresh leaf extract

21.5043.200.6303.561.472.092.9

22.7046.700.7253.911.562.356.2Dry leaf extract

Spraying

16.5038.200.3543.151.321.8312.5

18.9040.700.4253.431.432.0025.0Fresh leaf extract

16.5037.800.3502.240.891.352.9

18.3040.100.4103.291.401.896.2Dry leaf extract

Soil treatment

25.4051.000.8114.681.812.87500 ppmTralkoxydimHerbicide

25.7051.300.8514.711.822.89--Weed-free

11.5033.500.2111.880.851.03--Unweeded

1.812.730.0040.020.040.03LSD at 5%

Table 8 - Constituents of the essential oil in Eucalyptus citriodora

leaves

Dry leavesFresh leavesCompound (%)

56.461.5Citronellal

3.85.8Citronellol

0.91.1Citronellyl acetat

1.72.4β-caryophellene

1.32.3Isopulegol

3.53.9Neral

7.86.3Borneol

-1.1Geraniol

-4.6Eugenol

2.22.4P-cymene

2.82.2Lemonene

5.12.3Linalool

8.21.9α-pinene

Traces1.7Terpinene

6.10.5Unknown



896

was more effective in increasing totalcarbohydrate, as compared to the control. Totalcarbohydrate contents in bulbs were greatlyaffected by the different leaf extract andtralkoxydim treatments. It is evident thatE. citriodora extract treatments induced ahighly significant enhancement of the totalcarbohydrates in the plant bulbs. Totalcarbohydrate content was higher when

fresh extract was used, compared to the dryextract.

Nitrogen, phosphorus and potassium

contents

Figures 1 and 2 results indicate that therewere significant increases in the contents ofN, P and K in both amaryllis leaves and bulbs,

Figure 1 - Effect of different aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on nitrogen, phosphorus andpotassium contents of amaryllis leaves.

Figure 2 - Effect of different aqueous extracts of fresh and dry leaves of Eucalyptus citriodora on nitrogen, phosphorus andpotassium contents of amaryllis bulbs.

Soil treatmentsSpraying treatments

NP

K, %

Soil treatmentsSpraying treatments

NP

K, %



due to the treatments with the differentextracts sprayed or soil applied and herbicide.Significant high levels of N, P and K contentsin amaryllis leaves were recorded withspraying treatments, especially when thefresh leaf extract was used (Figure 1). Thecontents of N, P and K in amaryllis plant leavesundergoing the weed-free and herbicidetreatments surpassed all treatments,compared with the corresponding contents inthe unweeded control. In addition, there wasa significant increase in the contents of N, Pand K in amaryllis bulbs (Figure 2) with freshleaf extract spray of E. citriodora, which wasfound to have a better effect, compared to thecontents of the corresponding controls. Theincrease caused by weed-free control andherbicide application was higher.

Increases in different metabolic pathwayactivities such as chlorophyll synthesis and,consequently, total carbohydrates (Table 7)were concomitant with amaryllis growth.Significant increase in nutrient contents inleaves and bulbs (Figures 1 and 2) of amaryllisplants may be attributed to reduced weed/plant competition (Hussein, 2001) due to thetreatments with the previous extracts.

This work indicated that the leaf extractsof E. citriodora have the potential of actingas a natural herbicide against wild oat(Avena fatua) The fresh leaf extract ofE. citriodora which contains different volatileoil compounds was more effective than the dryleaf extract. Their effectiveness in controllingweeds may favor their use in agriculturalsystems, with a concomitant decrease in theneed for synthetic herbicides.

ACKNOWLEDGMENT

The authors thank the AgriculturalResearch Center in Giza, Cairo, Egypt forproviding amaryllis bulbs and help with thechemical analysis, and the Egyptian NationalResearch Center for facilitating this work.

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efeitos alelopáticos do eucalyptus citriodora sobre ...2007/2008). amaryllis plant cv. belinda...

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